High-quality imaging is of great interest for a wide range of applications. In the medical field in particular, where the health of the patient can depend on it, the best possible imaging is required for example as a basis for operations on the patient.
Normally, medical images are produced preoperatively, such as for example by means of computed tomography (CT), nuclear magnetic resonance tomography (NMR, MR, MRI, MRT), positron emission tomography (PET), single photon emission tomography (SPECT), ultrasound (US)—or on the other hand intra-operatively (io), such as for example by means of io CT, io MRI, io US or freehand SPECT. Recording of images is also known, for example the recording of an anatomical image (such as for example a CT-MRI or US image) using a functional image (such as for example a PET or SPECT image), i.e. an image which visualises the localised distribution of a function or a bodily activity. Such recorded images can for example help, in the case of tumour operations, to decide which tissue parts are to be excised on the basis of the anatomical and functional information. Images which are as up-to-date as possible and of the highest quality are desirable, as in such a manner it is possible to avoid damaging healthy tissue or not removing diseased tissue due to error.
Producing high-quality images places high requirements on detector data for imaging and on an evaluation system which must process these data. This is true in particular for the processing of detector data with movable detectors which are held/guided in the hand and/or which are located inside a cavity or a lumen of the body.
The prior art in the context of the present invention is disclosed for example in U.S. Pat. No. 6,602,488, U.S. Pat. No. 6,456,869, U.S. Pat. No. 6,317,622 or U.S. Pat. No. 6,167,296 and enables the tracking of hand-held probes as conventional diagnosis devices, in particular during a surgical intervention, and also tracking systems for determining the position and orientation of operating instruments and imaging devices.
The idea of tracking nuclear probes has already been disclosed in the past by a number of groups, for example as in U.S. Pat. No. 6,510,336 and U.S. Pat. No. 6,021,341. As furthermore disclosed in U.S. Pat. No. 6,643,538, nuclear probes can be designed to be integrated with a camera.
The output signal of nuclear probes is generally just a one-dimensional signal which is not temporally constant. The main advantages of such devices are the portability, simplicity and the possibility of the miniaturisation thereof for investigating cavities, for example when mounted on endoscopes. As each measurement is furthermore not limited to a certain position with respect to the preceding position, probes furthermore enable the scanning of any desired surfaces with a spatial precision which is only limited by the size of the sensor and the range of the detected nuclear radiation.
Nuclear probes, such as e.g. gamma and beta probes can measure the radioactive decay of radionuclides in tracers which are injected into the patient before the intervention. The disadvantage of these nuclear probes is the fact that one is concerned here with point measurements. This makes the weighting of the physical value on a surface more difficult if it changes considerably with position. A further problem in this case is the fluctuation of the measurement results, which is based on the statistical nature of the decay and detection process, which makes the interpretation of the measurement data difficult and potentially unreliable.
The use of probes of this type for combining position and orientation tracking with surface reconstruction and visualisation has been described in WO 2007/131561 A2. This method is known as freehand SPECT and is already used in the case of open surgical interventions, i.e. with the patient's body opened, and not by contrast in the minimally invasive field. Among other things, it includes measuring the emission of the target tissue using a nuclear probe with a detection characteristic essentially bundled in the longitudinal direction thereof, and also a comparison of this data with position information about the probe itself.
A disadvantage of all of the above-mentioned methods is the fact that the generally hand-guided nuclear probe delivers the data for an image calculated therefrom and that e.g. the quality of the image generated from the detected data may not be optimal or may be improvable due to a coincidentally unfavourable guiding of the probe by the user. This may be very difficult in the case of guiding endoscopic nuclear probes, where the movement options are very limited, inter alia due to guiding through the skin or through bodily orifices.
Against this background, the object of the present invention is to provide a system and method for intracorporeal imaging, particularly in the case of computer-controlled operation with nuclear probes, which delivers improved image quality compared to known methods.